Unstabilized .beta.-halopropyl esters of thionophosphoric acids are well known in the art. Their manufacture is disclosed in U.S. Pat. Nos. 2,866,805 and 2,984,681. Their use in gasoline as ignition control agents is disclosed in U.S. Pat. No. 2,862,950. The addition of these esters of thionophosphoric acids to crankcase lubricants is disclosed in DeWitt, U.S. Pat. No. 2,912,381.
The addition of various additives to base stocks of hydraulic fluids to modify certain properties of these base stocks is known in the prior art. For example, the various additives, as well as the base stocks, are described in R. E. Hatton, Introduction to Hydraulic Fluids, Reinhold Publishing Corporation, New York, N.Y.